1. Field of the Invention
The present invention relates to a current limiting circuit and a power regulator using the same, more particularly to, an active current limiting circuit and a power regulator using the same.
2. Description of the Prior Arts
Generally speaking, in the application for DC voltage regulators (Also known as “power regulator”), there will always be some corresponding protection circuits such as over voltage protection, over temperature protection, and over current protection, and said over current protection can be realized by a current limiting circuit. In the most of occasions, the current limiting mechanism takes advantage of the detection of the current running through the power transistor, and a resistor is used to convert the detected current into the voltage, and then the voltage turns on a P-typed transistor so as to clamp the gate voltage of said power transistor by a charging current. Thus, the loading current of the DC voltage regulator can be limited so as to achieve the over current protection.
Refer to FIG. 1 and FIG. 2, which depicted the conventional approaches. The disclosures of FIG. 1 relates to the conventional current limiting circuit for U.S. Pat. No. 7,362,080. In FIG. 1, a resistor RS100 detects the current flowing through a power MOS M101 and converts the detected current into a voltage to control a transistor M102. When the occasion of over current occurs, the voltage drop on RS100 is adequate to turn on said M102, that is; there will be a current flowing through M102 to clamp the gate voltage (VEO) of said M101 so as the goal of current limiting can be achieved. However, the most significant drawback for this approach is the minimum dropout voltage between the input side and output side of the voltage regulator will be enlarged.
FIG. 2 relates to an improved structure for the prior art of U.S. Pat. No. 7,362,080. In FIG. 2, a transistor MP203 is used to detect the current flowing through a power transistor MP201. When the occasion of over current occurs, the voltage drop on a resistor RS201 is adequate to turn on a transistor MP204, meanwhile, there will be a charging current to clamp the gate voltage of said MP201, in the similar manner, to achieve the goal of current limiting. However, the error caused by said resistor RS201 for process and temperature variation will directly affect the accuracy of the current limiting circuit.
Besides, since the conventional disclosures in both FIG. 1 and FIG. 2 relates to a resistive impedance, if desire to limit the current at a lower value, the resistor values must be enhanced and the corresponding die size will be also enlarged. To sum up, to enhance the accuracy for different processes and temperature variations and to improve the area efficiency for the chip area are both the important topics for the present invention.
Accordingly, in view of the above drawbacks, it is an imperative that an active current limiting circuit and a regulator using the same are designed so as to solve the drawbacks as the foregoing.